This invention relates to a method of, and apparatus for, determining the melting point of a powdered material.
In the following description the invention will be described mainly with reference to determining the melting point of coal ash or, more generally, the combustion product of a combustible material. It is to be understood however that other products which are powdered or particulate, for example sugar, can also be used in the method and apparatus of the invention.
The melting point of ash that is produced when coal is combusted in a furnace is of great importance. If the temperature within the furnace exceeds the melting point of the ash then the ash melts and in the liquid form adheres to surfaces inside the furnace. If this process continues the interior of the furnace is ultimately closed off and the through-flow of mateial through the furnace is impeded and the efficiency of heat transfer drops. In a severe case the furnace must be shut down and the fused deposits on the internal surfaces of the furnace must be mechanically removed for example by chipping.
A standardised technique is used to assess the melting point of a combustion product. In this technique the coal which is under test is placed in a flat dish and slowly allowed to burn to an ash at a comparatively low temperature. The ash is ground, moistened, and moulded into a small three-sided pyramid. The pyramid is carefully dried under controlled conditions and then placed in a furnace the temperature of which is gradually increased.
An operator monitors the pyramid by means of a special viewing device and records temperatures at which various events occur; for example the temperature at which the uppermost sharp point of the pyramid rounds off perceptibly, the temperature at which the pyramid slumps to a certain extent by proportion, and the temperature at which the pyramid flows and rounds off to a molten bead.
The standardised procedure described is laborious and time consuming and is subject to inaccuracies which arise inter alia from the observer's skills and experience, and from variations in the pyramid-making process.
The requirement for a human observer has been obviated by making using of electronic scanners which view the pyramid under test, and by using computers to process the ensuing data. The problems associated with the forming of the pyramid however remain.